1. Field of the Invention
This invention relates to a dry sump lubrication system which delivers a lubricant in an oil tank to moving parts to be lubricated in an engine by an oil pump, and returns the lubricant collected in an oil sump to the oil tank.
2. Description of Related Art
A single cylinder or two-cylinder engine with a large displacement generally causes a larger reciprocating mass of a piston and toque variations during a combustion stroke, compared to a multi-cylinder engine with the same displacement. Therefore, the single and two-cylinder engines tend to need a thick, large-diameter crank arm in order to increase the moment of inertia.
In addition, the single cylinder or two-cylinder engine with a larger cylinder internal volume inevitably has a larger crank throw radius and a longer piston stroke, compared to the multi-cylinder engine with the same displacement. Therefore, the single and two-cylinder engines tend to have an increased engine height. Specifically, a motorcycle, which has an engine mounted between front and rear wheels, a fuel tank disposed on the upper side of the engine, and a deriver's seat disposed on the rear end of the fuel tank, causes an increase in the motorcycle's engine height. This results in the fuel tank being provided in a higher position, causing the motorcycle to have a deteriorated appearance and an improper driver's position. Therefore, the motorcycle needs to reduce its engine height to a minimum.
In order to reduce the engine height, the motorcycle uses a dry sump lubrication system having a separate oil tank to which a lubricant accumulated at the bottom of a crankcase returns so that the bottom of the crankcase can be elevated to the crankshaft.
With the crankcase bottom elevated, the crankshaft rotation and piston reciprocation cause pressure variations. Therefore, the lubricant accumulated at the bottom of the crankcase is dispersed forward and rearward of the crankshaft, making it difficult to collect the lubricant. A motorcycle with a larger engine displacement shows a stronger tendency in this occuring. This prevents the motorcycle from having a larger engine displacement.
The advantage of the present invention made in view of the situation described above is to provide a lubrication system for an engine capable of reducing the engine height by elevating the crankcase bottom, as well as of reliably collecting a lubricant accumulated at the bottom of the crankcase.